Electron discharge device



Oct. 27, 1936. w. c. WHITE ET AL ELECTRON DISCHARGE DEVICE Filed July31, 1935 m 26 Inventors:

William C.Whi.te, Thomas AElcler,

Their Attornev.

Patented Oct. 27, 1936 UNITED STATES PATENT OFFICE ELECTRON DISCHARGEDEVICE Application July 31, 1935, Serial No. 33,990

7 Claims.

The present invention relates to electron discharge devices, and moreparticularly to an improved cathode mounting for such devices.

The development of improved glass to metal seals has now made itpractical to construct sealed envelopes for discharge tubes consistingwholly, or in part, of relatively thin sheet metal. Due to the greatflexibility of such materials as compared with glass, envelopesconstructed in this manner may be subject to considerable distortionupon evacuation or changes in heat distribution throughout the tube. Asa result of such distortion there is a tendency for electrode partsrigidly fixed with respect to the metal walls to be displaced from oneanother in accordance with any flexure of the walls. This isparticularly noticeable in connection with cathode structures in whichthe heating element is supported at some distance from the tube wall. Insuch a case any deflection of the tube wall is greatly magnified inbeing transmitted to the cathode due to the great length of the cathodesupporting elements, thus resulting in an increase or decrease in thecathode position or dimensions. In tubes of the type with which ourinvention is chiefly concerned these variations are of considerableimportance since they may result in a change in the heating currentrequired by the cathode beyond the limits considered permissible forsatisfactory operation.

It is, therefore, an object of our invention to provide a practicalbracing means which will prevent objectionable displacement of theelectrodes. For attaining this object we provide a rigid member in thenature of a fixed beam having an externally accessibleforce-transmitting connection with the portion of the flexible envelopewall on which the electrodes are supported. By this means it is possiblenot only to prevent undesired displacement of the parts due to pressurevariations, but also to produce a corrective adjustment in the nature ofan artificial displacement where such an effect is desirable.

The novel features which we consider to be characteristic of ourinvention will be pointed out with particularity in the appended claims.Our invention itself, however, will best be understood by reference tothe following specification taken in connection with the drawing, inwhich Fig. 1 represents a sectionalized view of a tube structure whichwe consider suitable for the practice of our invention; Fig. 2 is ahorizontal section taken on line 2-2 of Fig. 1, while Fig. 3 is a planview of the tube shown in Fig. 1, Fig. 4 illustrates in section asomewhat modified tube structure embodying another aspect of ourinvention, while Fig. 5 is a section taken on line 55 across the tubeshown in Fig. 4, Fig. 6 being a partial plan view of the tube. Fig. '7is a fragmentary detail view of the force-transmitting connection ofFig. 4.

Referring more particularly to Fig. 1, we have illustrated a dischargedevice comprising 2. cylindrical envelope l which may convenientlyconsist of a section of seamless steel tubing. This may be sealed at thetop by a flanged diaphragm 2, line-welded or otherwise hermeticallysealed to the interior surface of the cylinder. In view of theconducting nature of these parts, it is considered practical to use theenvelope itself as the positive electrode or anode of the discharge pathalthough separate electrode structure may be alternatively provided forthat purpose. The envelope may either be highly evacuated or providedwith a quantity of an ionizable medium such as an inert gas or mercury,depending on the purposes for which the device is to be employed.

Supported between the ends of the cylinder l and spaced from its wallswe have illustrated a directly heated cathode 3 shown as consisting of aconvoluted or pleated expansible metal ribbon. Numerous materials may beused for the construction of the cathode, but we prefer to use a basemetal such as nickel or tungsten suitably coated with an alkaline earthmetal oxide or other electron emissive substance. The cathode 3 isdirectly mounted on a pair of supports 4 and 5 which may be ofheat-resisting conducting material such as nickel. These in turn arefurther supported on heavy conducting copper or steel rods 6 and l,silver soldered, brazed or welded at their lower extremities to a pairof inverted thimbles 8 and 9. The thimbles should be of a materialcapable of being fused directly to glass and suitable for the formationof a gas-tight glass to metal seal. A seal of this type and materialsuitable for its manufacture is fully described and claimed inapplication, Serial No. 716,111 to H. J. Nolte, filed December 26, 1933,and assigned to the same assignee as the present invention. The natureof the seal not being material to the structure of our invention, it isnot considered necessary to describe it with greater particularityherein.

Connections to external lead-in conductors iii and II are made bysuitably affixing their ends to the under surfaces of the thimbles 8 and9, respectively. For the purpose of increasing the arc-over resistanceof these connections insulat- 55 ing cylinders l2 and I3 are looselyplaced over the lead-in wires. These may conveniently consist of glassor equivalent vitreous material and serve to minimize the danger ofrandom contacts or corona discharge.

The lower end of the envelope I is closed by a flanged diaphragm l4suitably sealed at its outer periphery to the interior of the maincylinder and so positioned that a portion of the cylinder projectssubstantially beyond the diaphragm. For bringing the lead-in conductorsto the interior of the seals a pair of apertures l5 and I6 are formedhaving their centers on a diameter of the diaphragm M in such a positionas to be aligned with the supporting rods 6 and l. A dependingtubulation l9 serves as a convenient means for exhausting the tube andalso as a condensation reservoir in case the tube is desired to beoperated with a mercury vapor filling.

It will be apparent that with the structure so far described aconsiderable degree of flexibility is available due to the relativethinness of the diaphragm M. For this reason when the envelope l issubjected to a high vacuum exhaust the effect of the decrease ininternal pressure is to cause an initial fiexure of the diaphragm wallto a position such as that shown in dotted outline at H. The directresult of this displacement is to destroy the parallelism supposed toexist between rods 6 and l and to increase the degree of extension ofthe cathode 3, causing it to assume a new form such as is shown at l8.Since the operating characteristics and particularly the temperature ofa cathode ribbon such as that illustrated depends largely upon thedegree of mutual shielding provided by adjacent convolutions, it will beobvious that a considerable change in these factors may be occasioned bythe displacement indicated. Very frequently the magnitude of the changethus brought about will be so great as to render the tube unsuitable forthe circuits for which it is designed.

To overcome this difliculty and to permit regulation of the cathodeextension our invention provides a bracing structure associated with thecathode supports for preventing fiexure of the diaphragm I4. For thispurpose we prefer to use a bar of insulating material 20 positionedwithin the confines of the projecting cylinder portion and diametricallytraversing the exterior surface of the diaphragm in such a way as topass under the horizontal projections of the rods 6 and l. The outerends of the bar 20 should be either in contact with the diaphragm l4near its outer periphery or kept in fixed relation thereto by a suitablespacing means. The central portions of the bar and diaphragm should,however, be appreciably spaced to allow relative motion between them.

In view of the above description it will be seen that the bar 20 is ineffect a beam supported at its ends. For utilizing this structure as ameans of adjusting the displacement of the cathode supports we provide aforce-transmitting connection in the form of a bolt 2| which passesthrough the beam at the central portion thereof and is affixed at oneend to the diaphragm M by a butt-weld, or other rigid connection. Theouter extremity of the bolt is threaded and furnished with a nut 22which may be alternatively tightened or loosened to vary the amount offorce exerted on the diaphragm.

It will be understood that if the condition of the tube after exhaust issuch as to cause the cathode to tend to assume the position shown at l8,it may be restored to a proper displacement simply by tightening the nut22. The tightening may be accomplished before exhaust, in which case thebeam 20 and the bolt 2| act as an anchoring means, or it may betightened after exhaust, the tightening operation then being in thenature of an adjustment. If the latter method is used the properadjustment may be obtained either by observing the actual positioning ofthe parts as by means of an X-ray equipment or other convenientobservation mechanism, or by noting the variations of the current drawnby the cathode at a constant voltage. Since this last value is in eifectproportional to cathode resistance and, hence, to the degree of cathodeextension extremely accurate regulation may be accomplished in this way.

The beam 20 may be constructed of any material having good mechanicalstrength and insulating properties. We have found it convenient to usefor this purpose refractory material comprising a mixture of from 70 toper cent of magnesium silicate, or talc with a complementary portion ofclay and feldspar. When properly mixed, compressed and fired, thiscomposition yields a product having a tensile strength of approximately10,000 pounds per square inch. In addition, it is of high insulatingquality, nonhygroscopic and eminently suited to the purposes of ourinvention.

In order to prevent rotation of the beam 20 when torque is applied tothe nut 22, it is advisable to provide upset projections such as thoseshown at 23 and 24 to engage the diaphragm apertures l5 and Hi. We havealso found it convenient to provide holes in the beam structure topermit the passage therethrough of. the lead-in conductors l0 and I I.In this way besides the functions described above, the beam is made toserve as an insulator for maintaining the bare conductors inappropriately spaced relation.

For some purposes it may be desirable to provide means for exerting bothan expanding and a contracting force on the cathode 3. The value of suchan arrangement might be realized, for example, in cases Where theconditions of manufacture are such that the cathode ends tend to assumetoo close a displacement. To allow for this possibility and to makepossible an even greater degree of adjustment than is permissible withthe structure already described, we have illustrated a modification ofwhich our invention is capable. This is shown in detail in Figs. 4, 5and 6 in which parts corresponding to those illustrated in Fig. l areidentically numbered.

In connection with Fig. 4 it will be noted that the beam 20 is cut awayover a considerable portion of its length to permit of great relativemovement of the diaphragm H. In this embodiment as in that of Fig. 1 theforce transmitting connection takes the form of a bolt 2| secured to thediaphragm at its inner end. The tightening nut, however, consists of apair of spaced enlargements 25 and 26 interconnected by a section 28a ofsmaller diameter which is keyed into an anchor plate 21, this in turnbeing rigidly bolted or otherwise secured to the lower face of the beam20. The details .of this construction may readily be understood by aninspection of. the enlarged view of Fig. 7.

With the arrangement just described above both thrust and tensile forcemay be transmitted to the central portion of the diaphragm l4, and theextension of the cathode varied between the extreme limits designatedbythe full line position shown at 28 and the dotted line position shown at29. Since the cathode supports are approximately symmetrically disposedwith respect to the movable portion of the diaphragm, a slight movementof the latter will produce a magnified motion of the ends of the cathodesupports remote from the diaphragm. To prevent rotation and outwardmotion of. the beam 20 during the application of the adjusting force,retaining studs 30 may be bent out of the flanged portion of thediaphragm I4 and pressed into corresponding slots in the face of thebeam.

It is a particular advantage of the structural arrangements which wehave described that deviations in cathode operation attributable toslight variations in material or errors in construction may be readilycompensated. Thus, in a tube which is found to draw too little heatingcurrent when first tested the cathode extension may be increased evenbeyond the normal position in order to correct the defect. This featuremakes possible a degree of manufacturing uniformity heretofore entirelyunavailable in connection with glass and other tubes of more rigidconstruction. In testing such tubes a specimen found defective musteither be rejected as imperfect or completely rebuilt. By utilizing thestructure of our invention on the other hand, a relatively simpleadjustment will cause the tube characteristics to conform to therequired operating standards.

While we have shown a particular embodiment of our invention, it will ofcourse be understood that we do not wish to be limited thereto sincemany modifications in the structure may be made, and we contemplate bythe appended claims to cover all such modifications as fall within thetrue spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States, is:

1. In an electric discharge device, a sealed cylindrical envelope havinga flexible diaphragm closing one end thereof, electrode supports mountedon said diaphragm, a rigid beam diametrically traversing said diaphragm,said diaphragm being fixed with respect to said beam only adjacent theends thereof and a force transmitting connection between said beam andsaid diaphragm at the center thereof.

2. In an electric discharge device, an extensible cathode, conductivesupporting elements secured to the ends of said cathode, and meansassociated with said elements for varying at will the extension of saidcathode, said means being accessible externally of said dischargedevice.

3. In an electric discharge device, a pleated extensible cathodesupported at its ends, a sealed envelope enclosing said cathode andconsisting in part of a flexible diaphragm, supporting connectionsbetween the ends of said cathode and said diaphragm, and meansassociated with said diaphragm for varying the extension of saidcathode.

4. An electrode mounting comprising a flexible diaphragm having aplurality of apertures therein, gas-tight lead-in seals associated withsaid apertures, a rigid beam traversing said diaphragm and having upsetprojections engaging said apertures, said diaphragm being fixed withrespect to said beam only at its ends, and a force transmittingconnection between said diaphragm and said beam intermediate the endsthereof.

5. In an electric discharge, device, an extensible cathode whoseoperating characteristics are variable with the extension thereof, asealed envelope enclosing said cathode and consisting in part of aflexible diaphragm, supporting connections between the ends of saidcathode and said diaphragm, a bracing member mounted adjacent saiddiaphragm and a force transmitting connection between said member andsaid diaphragm for flexing the latter to vary the extension of saidcathode.

6. In an electric discharge device, a sealed envelope consisting in partof a flexible diaphragm, a bracing member rigidly mounted adjacent saiddiaphragm, said diaphragm having a portion thereof freely movable withrespect to said bracing member, a pluraltiy of electrode supportsmounted on said diaphragm at positions approximately symmetricallydisposed with respect to said movable portion and an adjustableforcetransmitting connection between said member and said movableportion for fixing the position of the latter thereby to determine thespacing of the ends of said electrode supports remote from saiddiaphragm.

7. In an electrical discharge device, a sealed envelope including anelongated metal cylinder, a flexible diaphragm inset in one end of saidcylinder so as to leave a portion of the cylinder projecting beyond thediaphragm, electrode supporting means mounted on the inner surface ofsaid diaphragm, a rigid beam positioned within the confines of saidprojecting cylinder portion and traversing the outer surface of saiddiaphragm and a force-transmitting connection between said beam and acentral region of said diaphragm.

WILLIAM C. WHITE. THOMAS A. ELDER.

